Hearing instruments, i.e., devices that assist the hearing impaired, designed for complete or partial insertion into the user's ear canal, have a shell or housing that holds various components. One such component is the receiver, which generates the sound heard by the hearing instrument's user. The sound is carried from the receiver by a receiver tube affixed to a port on the receiver to an opening (the receiver tube hole) in the tip of the shell, the portion of the hearing instrument positioned in the ear canal towards the eardrum.
Another feature of a hearing instrument is a vent, a conduit from the inner ear to the outside. When a person speaks, vibration is generated in the bone structure of their head, creating sound pressure in the inner ear. Normally, this sound pressure escapes if the ear canal is not occluded. However, if a hearing instrument is inserted into the ear, occluding the ear canal, the hearing instrument user will perceive an unpleasant, hollow sound, a phenomenon known as the occlusion effect. A hearing instrument vent will provide relief, allowing at least some of the sound pressure to escape from the inner ear. A vent also permits the pressure in the ear to equalize with respect to the outside when the hearing instrument is inserted into the ear. An opening provided in the shell tip serves as the inlet for the vent.
If the hearing instrument shell is small in size, there may not be sufficient room to accommodate the full diameters or cross-sections of both the receiver tube hole and the vent hole, and the underlying receiver tube and vent. (The receiver tube and the vent may have circular cross-sections or any other suitable cross-section.) Some arrangement is then required to provide room for the receiver tube and vent in the shell tip, as well as openings for the receiver tube and the vent on the surface of the shell tip, such that they do not interfere with each other.
A Tapered Vent
By reducing the cross-section of the vent tube near the tip of the shell, the vent hole can be made smaller, allowing for a receiver tube hole equal to the full cross-section of the receiver tube. A reduction in the cross-section may be achieved by introducing a taper to the vent as it reaches the end of the tip and the vent hole or otherwise providing a vent of smaller cross-section. The cross-section of the vent is reduced only in the vicinity of the tip, preserving its full cross-section elsewhere in the instrument. Computer-aided design (CAD) techniques, including Boolean operations, may be utilized to create the smaller vent and vent hole.